Align vertices in straight line in the uv image editor
You can select all vertices in a row by using alt+ RMB on an edge;



You can align selected vertices on the x axis with the following keystrokes (one after the other, not all at once);

s, x, 0, enter



Same for the Y axis, select with alt+ RMB



s, y, 0, enter



(those are zeros, not the letter o)

Continuing this process, you can align the desired vertices on x...;



Then y...;